1. Field
The present disclosure pertains to a vertical top-fed grain mill (degermer). More particularly, the present disclosure relates to a grain milling machine which causes intermittent compression of grains while reducing potential overmilling.
2. Description of the Related Art
Milling machines are well known wherein grains, such as corn kernels, are debranned and the germ freed or exposed by application of impact force. Grains are supplied from a feeding inlet to a milling chamber having a milling roll, which serves as an impeller and which typically has an abrasive surface. The grains are then circulated by the milling roll, induced to move due to contact with the milling roll's abrasive surface, and are milled until exiting. The milling roll may include one or more agitating projections or stirring bars mounted on the milling roll within the milling chamber and/or may be elliptical to circulate the grains within the mill. During circulation, the grains rub one another, causing the bran layer to separate from the endosperm and germ. If the distance between the exterior of the milling roll and the milling chamber varies, such as by use of an elliptical milling roll or by use of a polygonal screen defining the exterior of the milling chamber, the grains within the milling chamber are additionally intermittently compressed, increasing the friction between the grains and increasing the internal stresses within the grains, thereby speeding bran removal and grain fracturing, respectively. Typically, a screen defines the extent of the milling chamber. The screen includes perforations to permit grain fragments, generally referred to as brokens, which may be germ, endosperm, bran or a combination thereof, of less than a maximum size, to exit the milling chamber. The force applied to the grains and the associated speed of processing may also be affected by selection of the size, density and direction of the perforations. Additionally, breaks or breaker bars may be installed about the screen that produce further localized areas of compression, which result in further fracturing of the kernels, or propagation of existing fractures within the kernels. Sufficient milling for exposing germ or for reduction of the grain broken size may be controlled by requiring a minimum force be applied to a discharge gate by or through the adjacent grains. Removal of sufficiently milled kernel brokens prior to reaching the top of the milling chamber may be permitted by sufficiently sized perforations in the screen. Those brokens passing through the screen are known as throughs. The grains and brokens passing through the mill to the output are known as overtails.
Various milling systems are known in the art for milling of grains. Some mills are horizontally aligned, wherein grains are input at one end of a horizontal-oriented mill, travel horizontally during milling and then exit. The Beall-type degermer is one such well-known horizontally-oriented mill. In a Beall-type degermer, corn is fed into and through the annulus at one end and between a rotating, conical rotor and a stationary concentric screen made of perforated metal. Both rotor and screen are textured with large nodes, which impede motion of the kernels as they are impelled by the rotor.
Other mills are vertically-aligned, wherein grains are input at the top or the bottom of a vertically-oriented mill, travel downward or upward, respectively, during milling and then exit One such machine is the Satake Maize Degermer VBF. During rotation of the milling rotor in a vertical degermer, the corn is circulated horizontally by the milling rotor and is retained by the surrounding screen while moving in the vertical plan.
In both type of mills, as bran layers may remain with the pieces of endosperm after processing, further refinement may be necessary to reduce the fiber content of the endosperm product.
Problematically, grains that are sufficiently fractured early in the milling process continue to be milled with insufficiently fractured grains, often resulting in excessive milling and thereby degradation of products. It is generally desirable to minimize the production of fine particles, known as “fines” as these fines are difficult to separate in order to recover as a marketable product. One resolution has been the positioning of breaker bars at the section of the screen adjacent the discharge to accelerate fracturing of the kernels immediately prior to discharge. The breaker bars may substantially affect the output and milling time, as well as the power applied by the milling roll to the grains.
In horizontal mills and vertical bottom-fed mills, a substantial amount of energy is required for milling, which includes the energy needed to introduce grains to the machine and to drive already-present grains toward discharge. Vertical top-fed mills may avoid this issue by introducing grains at the top, but must then address the problem of increased milling resulting from the weight of the newly introduced grains atop those grains already being processed in connection with the abrasive roll.
Frequent screen replacement is typical in these mills, particularly as the screen surrounding the milling chamber wears, and often wears unevenly, particularly adjacent the point of introduction of the grains. The constant abrasion of the grains wears the periphery of the perforations of the screen. Such wear requires frequent screen replacement even though the remaining portions of the screen remain usable.
Thus, there is a need in the art for vertical grain mill which sufficiently mills grain at high rates of processing while addressing shortcomings of the prior art.